1. Field of the Invention
The present invention relates, in general, to micro-electro-mechanical system (MEMS) packages with side sealing members and methods of manufacturing the packages and, more particularly, to an MEMS package and a method of manufacturing the package, in which a sealing member is formed on a side surface of a lid glass that is mounted on a spacer surrounding MEMS elements provided on a base substrate and covers the MEMS elements, so that the sealing member hermetically seals the MEMS elements from the external environment.
2. Description of the Related Art
In recent years, high-capacity communications for broadband service, such as in the Internet or the IMT 2000, have become powerful, so that optical communication technique including, for example, WDM (wavelength division multiplexing), has been quickly standardized. In relation to the standardization of the optical communication technique, MEMS, which does not depend on wavelength, data rate or signal format and thereby has characteristics of being “optically transparent”, has been proposed and recognized as an innovative technique to supplant electronics, which can accomplish the recent trend of system smallness.
In the related art, current applications of MEMS are accelerometers, pressure sensors, inkjet heads, hard disk heads, projection displays, scanners and micro-fluidics. In recent years, interest in the technique of optical communication elements with higher operational performances to meet the rapid development in the optical communications field has increased.
Particularly, the interest in the technique of the optical communication elements is concentrated to spatial light modulators, which have a great number of micromirrors and operate in a specified switching manner that the micromirrors are actuated by MEMS type actuators. The spatial light modulators use an optical signal processing technique with advantages in that a great amount of data can be quickly processed in a parallel manner, unlike a conventional digital information processing technique, in which a great amount of data cannot be processed in real time.
Thus, studies have been actively conducted on the design and production of binary phase only filters, optical logic gates, light amplifiers, image processing techniques, optical devices, and light modulators using the spatial light modulation theory. Of them, the spatial light modulators are applied to optical memories, optical display devices, printers, optical interconnections, and hologram fields, and studies have been conducted to develop display devices employing the spatial display modulators.
However, the MEMS elements have ultra-fine actuators so that the MEMS elements are greatly sensitive to the external environment, including temperature, humidity, micro-dust, vibration and impact, and thereby may frequently commit errors during operation or suddenly stop operation.
In an effort to allow the MEMS elements to effectively operate without being negatively affected by the environment, the MEMS elements have been sealed in cavities of sealed packages. U.S. Pat. No. 6,303,986 discloses a method and apparatus for sealing MEMS elements using a hermetic lid to provide an MEMS package.
Herein below, the construction of the MEMS package disclosed in U.S. Pat. No. 6,303,986, in which the lid glass hermetically seals the MEMS elements from the external environment, will be described with reference to FIG. 1.
FIG. 1 shows a representative sectional view of the MEMS package in which the transparent lid hermetically seals the MEMS element. As shown in FIG. 1, a conductive ribbon 100 having a metallic conductive/reflective covering 102 is formed over an upper surface of a semiconductor substrate 104, with an air gap 106 defined between the ribbon 100 and the substrate 104.
A conductive electrode 108 is formed on the upper surface of the substrate 104 and covered with an insulation layer 110. The conductive electrode 108 is placed under the ribbon 100 at a position under the air gap 106.
The conductive/reflective covering 102 extends beyond the region of the mechanically active ribbon 100 and is configured as a bond pad 112 at its distal end. The MEMS package is also passivated with a conventional overlying insulating passivation layer 114 which does not cover the bond pads 112 or the ribbon structures 100 and 102.
Control and power signals are coupled to the MEMS package using conventional wire-bonding structures 116.
Unlike conventional semiconductor manufacturing techniques in which semiconductor elements are packed densely onto the upper surface of a semiconductor substrate, an optical glass is hermetically sealed directly onto the semiconductor substrate in the above-mentioned US patent. Thus, the bond pads 112 are spaced a considerable distance from the ribbon structures 100 and 102, so that a lid sealing region 118 is provided. A solderable material 120 is formed onto the lid sealing region 118.
The hermetic lid 122, which is joined to the semiconductor substrate, is preferably formed of an optical quality material. Thus, the lid 122 can be used for a variety of purposes including filtering undesired radiation, enhancing reflectivity, or decreasing reflectivity.
The lid 122 may be also coated with an optically sensitive material to be used for other purposes without being limited to the above-mentioned purposes.
Once the lid 122 is formed to a size appropriate to fit concurrently over the lid sealing region 118, with a solderable material 124 formed in a ring surrounding the periphery of one surface of the lid 122, solder 126 is deposited onto the solderable material 124 so that the lid 122 is joined to the semiconductor substrate.
Though not shown to scale in the drawing, a significant space exists between the lid 122 and the ribbon structures 100 and 102 to prevent them from interfering with one another. Thus, the ribbon structures 100 and 102 are free to move upwards and downwards.
FIG. 2 shows a plan view of an exemplary package disclosed in the above-mentioned US patent wherein various regions are shown as blocks. As shown in the drawing, the ribbon structures of a GLV (diffraction grating light valve) to be used as a display engine comprise a mechanically active region 140, while the lid sealing region 118 surrounds the mechanically active region 140.
In this case, the lid sealing region 118 is passivated and includes no mechanically active elements, such as those traditionally found in MEMS devices.
Furthermore, the lid sealing region 118 includes no bond pads where other off-chip interface structures, such as the lid 122, would interfere with the effective operation of the MEMS device. However, it is possible that the lid sealing region 118 could include active electronic elements. In the event that the lid sealing region 118 did include active electronic elements, effort must be taken to planarize that region in order to provide the surface to which the lid 122 can properly mate.
The bonding region 142 surrounds the lid sealing region 118, and includes several bond pads 114 necessary for making interconnection from the package to off-chip circuits and systems.
Herein below, the method of sealing a hermetic lid to a semiconductor substrate to provide an MEMS package will be described in detail with reference to FIGS. 3a and 3b. 
As shown in FIG. 3a, a first solderable material 150 is formed onto the lid sealing region 152 of the semiconductor substrate 154. A second solderable material 156 is also formed around the peripheral edges of the transparent lid 158. Thereafter, a layer of solder 160 is formed over the layer of second solderable material 156.
The transparent lid 158 is brought into contact with and aligned to the semiconductor substrate 154 to provide an assembly. Heat is applied to the assembly, thus allowing the solder 160 to be melted.
In that case, surface tension of the melted solder 160′ causes the solder 160′ to remain between the first solderable material 150 on the semiconductor substrate 154 and the second solderable material 156 on the transparent lid 158.
Thereafter, the assembly is heated for a sufficient time to allow the solder 160′ to flow and wet all solderable surfaces. Once the heat is removed, the solder 160′ is re-solidified and the transparent lid 158 is hermetically sealed to the semiconductor substrate 154 as shown in FIG. 3b. 
However, in the above-mentioned method of sealing the semiconductor elements in the MEMS package, the solder must be placed between the substrate and the lid and, thereafter, heat must be applied to the solder through a reflow process at a predetermined temperature so as to bond the lid to the substrate. Thus, the method undesirably reduces the work speed to cause a reduction in productivity.
Another problem of the above-mentioned method is that it is impossible to execute a reworking process, such as for adding solder, even when the sealing is not complete due to inaccurate positioning of the solder and/or application of a deficient amount of solder to the junction between the substrate and the lid.